misc/wasm: pollute global JS namespace less

This commit changes wasm_exec.js so it only puts the single
name "go" into the global namespace. Other names became private
or were turned into a property/method of "go".

Change-Id: I633829dfd3c06936f092c0a14b9978bf855e41fe
Reviewed-on: https://go-review.googlesource.com/112980Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Agniva De Sarker <agniva.quicksilver@gmail.com>

misc/wasm/wasm_exec.html

@@ -17,14 +17,14 @@ license that can be found in the LICENSE file.
 		async function loadAndCompile() {
 			let resp = await fetch("test.wasm");
 			let bytes = await resp.arrayBuffer();
-			await compile(bytes);
+			await go.compile(bytes);
 			document.getElementById("runButton").disabled = false;
 		}
 
 		loadAndCompile();
 	</script>
 
-	<button onClick="console.clear(); run();" id="runButton" disabled>Run</button>
+	<button onClick="console.clear(); go.run();" id="runButton" disabled>Run</button>
 </body>
 
 </html>